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TL;DR: Using an upgraded (and fixed) Parallel Build Process Template allows to use multiple TFS2012 build agents simultaneously, which can be more than welcome when building metro apps that target all three supported platforms. A build that took 11 minutes can go down to 3.5 minutes.

CI is a wonderful feature, especially when associated with Gated Checkins.

You’re certain that what’s in your source control is in line with your build definition and constraints, and that there is always a binary that respects a minimum set of rules. This does not ensure that your app is bug free, but still, that’s a minimum.

Build time matters

The downside of this validation is that there cannot be multiple builds running at the same time. This can become a bottleneck when multiple developers checkin within the duration of a single build run.

This means that the longer your build gets, the longer a developer might wait for its task completion because of a long build queue, and increase its task switching cost. If a build fails, the developer needs to unshelve its changes, make the necessary adjustments, then check-in again.

Below 4 minutes of build time, this stays in the acceptable range where the developer’s task context may not be lost if the build fails.

TL;DR: The JIT can take over a third of the startup time of a managed Metro App, and using Native Image Generation (NGEN) can greatly improve the startup time of these apps. There is also a way to check for these native images to act accordingly.

Now that the Surface RT devices are available, we’re facing quite a few challenges in terms of code execution performance, and I’m going to discuss a few tips and tricks about the Managed Code JIT on Windows RT.

Profiling a slow starting app on a Surface RT

Running apps on the Surface can be troubling. Having an app that is useable after 16 to 18 seconds is definitely not acceptable, let alone the fact that the Splash Screen can disappear after 6 to 8 seconds.

Profiling such an app that starts slowly is very interesting, when looking a the Visual Studio profiler, where during these 17 seconds, about a third is spent in a “clr.dll” module in exclusive time (time spent only in this module and not its descendants). This is a very big number.

This time is actually spent in the JIT, where big methods tend to take more time to be JITed, sometimes on the UI thread, making the app sluggish.

As would say this guy, since you’ve most probably been using threads the wrong way (as Microsoft seems to think), you won’t be able to use the Thread class anymore in Metro Style applications. The class is simply not available anymore, and neither are Timer or ThreadPool.

That may come a shock to you, but this actually makes a lot of sense. But don’t worry, the concept of parallel execution is still there, but it takes the form of Tasks.

Why using Threads is not good for you

Threads are very powerful but there are a lot of terrible gotchas that come with it :

People tend to use Thread.Sleep to arbitrarily wait for some constant time that will most probably be incorrect, and that will waste CPU resources to manage a thread that does not do anything while it waits,

People tend to come up with complex designs to chain operations on threads, which most of the time fail miserably.

There are some more, but these a main scenarios where using Threads fall short.

TL;DR: This article talks about an app startup error that can happen with Metro Style apps in Windows 8, how the presence of an app.config file can prevent the app from starting and how the Windows event log viewer’s new Immersive-Shell section can help.

The Windows 8 Metro style Xaml/C# application development is an interesting experience.

Since .NET is merely on top of a WinRT and its native structure, you’re left in a bit of a darkness sometimes, when it comes to debugging problems that come from WinRT.

You’ve basically left at guessing, particularly on Windows Phone and Silverlight for the desktop, and if you’re lucky enough you’re having a error code that specific enough so that you can narrow your solution to a dozen google can find for you. If you’re not, well you’ve got a E_ERROR. Fail, as they say.

Windows 8 is actually a bit better at that, because of the Event Viewer. There’s a lot of details that appear there, and it’s very informative.

TL;DR: This article talks about the internals of the WinRT/Xaml implementation in Windows 8 and how it deals with databinding, its use of the IXamlMetadataProvider interface, tips & tricks around it, and how to extend the resolver to create dynamic databinding scenarios.

Xaml has been around for a while, and it’s been a big part of Silverlight and WPF. Both frameworks are mostly managed, and use a CLR feature known as Reflection, or type introspection.

This is a very handy feature used by Silverlight/WPF to enable late binding to data types, where strings can be used to find their actual classes counter-parts, either for value converters, UserControls, Data-Binding, etc...

The burden of .NET reflection

It comes with a cost, though. Reflection is a very expensive process, and up until very recently in Silverlight, there was no way to avoid the use of Reflection. The recent addition of the ICustomTypeProvider interface allows for late binding without the use of reflection, which is a big step what I think is the right direction. Having this kind of interface allows for custom types that define pre-computed lists of fields and properties, without having the runtime to load every metadata available for an object, and perform expensive type safety checks.

This burden of the reflection is particularly visible on Windows Phone, where it is suggested to limit the use of DataBinding, which is performed on the UI thread. The Silverlight runtime needs to walk the types metadata to find observable properties so that it can properly perfrom one or two-way bindings, and this is very expensive.

There are ways to work around this without having ICustomTypeProvider, mainly by generating code that does everything the Xaml parser and DataBinding engines do, but it’s mainly experimental, yet it gives great results.

WinRT, native code and the lack of Reflection

In Windows 8, WinRT is pure native code, and now integrates what used to be the WPF/Xaml engine. This new engine can be seen at the cross roads of Silverlight, WPF and Silverlight for Windows Phone. This new iteration takes a bit of every framework, with some tweaks.

These tweaks are mainly related to the fact that WinRT is a native COM based API, that can be used indifferently from C# or C++.

For instance, xml namespaces have changed form and cannot reference assemblies anymore. Declarations that used to look like this :

xmlns:common="clr-namespace:Application1.Common"

Now look like this :

xmlns:common="using:Application1.Common"

Where the using only defines the namespace to be used to find the types specified in the inner xaml.

Additionally, WinRT does not know anything about .NET and the CLR, meaning it cannot do reflection. This means that the Xaml implentation in WinRT, to be compatible with the way we all know Xaml, needs to be able to do some kind of reflection.

Meet the IXamlMetadataProvider interface

To be able to do some kind reflection, the new Metro Style Applications profile generates code based on the types that are used in the Xaml files of the project. It takes the form of a hidden file, named XamlTypeInfo.g.cs.

That file can be found in the “obj” folder under any Metro Style project that contains a Xaml file. To find it, just click on the “Show all files” button at the top of the Solution Explorer file. You may need to compile the project for it to be generated.

In the entry assembly, the file contains a partial class that extends the App class to make it implement the IXamlMetadataProvider interface. WinRT uses this interface to query for the details of types it found while parsing Xaml files.

This type acts as map for every type used in all Xaml files a project, so that WinRT can get a definition it can understand, in the form of IXamlType and IXamlMember instances. This takes the form of a big switch/case construct, that contains string representation of fully qualified types. See this example :

Note that if you want to step into this code without the debugger ignoring you, you need to disable the “Just my code” feature in the debugger options.

Also, in case you wonder, the Code Generator scans for all referenced assemblies for implementations of the IXamlMetadataProvider interface, and will generate code that will query these providers to find Xaml type definitions.

Code Generation is good for you

Now, this code generation approach is very interesting for some reasons.

The first and foremost is performance, because the runtime does not need to use reflection to determine what can be computed at runtime. This is a enormous performance gain, and this will be beneficial for the perceived performance as the runtime will not waste precious CPU cycles to compute data that can be determined at compile time.

More generally, in my projects, I've been using this approach of generating as much code as possible, to avoid using reflection and waste time and battery on something that can be only done once and for all.

The second reason is extensibility, as this IXamlMetadataProvider can be extended to add user-provided types that are not based on DependencyObject. This is an other good impact on performance.

Adding custom IXamlMetadataProvider

It is possible to extend the lookup behavior for standard types that are not dependency objects. This opens the same range of scenarios that ICustomTypeProvider provides.

All that is needed is to implement the IXamlMetadataProvider interface somewhere in an assembly, and the code generator used for XamlTypeInfo.g.cs will pick those up and add them in the Xaml type resolution chain. Note that for some unknown reason, it does not work in the main assembly but only for referenced assemblies.

Every time the databinding engine will need to get the value behind a databinding expression, it will call the IXamlMetadataProvider.GetXamlType method to get the definition of that type, then get the databound property value.

A very good feature, if you ask me.

The case of hidden DependencyObject

By hidden dependency properties, I’m talking about DependencyObject types that are not directly referenced in Xaml files. This can be pretty useful for complex controls that generate convention based databinding, such as the SemanticZoom control, that provides a implicit “Key” property to perform the Zoomed out view.

Since this XamlTypeInfo.g.cs code is generated from all known Xaml files, this means that these hidden DependencyObject types that do not have code generated for them. This forces the CLR to intercept these failed requests and fallback on actual .NET reflection based property searching for databinding, which is not good for performance.

This fallback behavior was not implemented in the Developer Preview, and the binding would just fail with a NullReferenceException without any specific reason given to the developer.

The case of Xaml files located in another assembly

If your architecting a bit your solution, you’re probably using MVVM or a similar pattern, and you’re probably putting your views in another assembly.

If you do that, this means that there will not be any xaml file in your main assembly (aside from the App.xaml file), leading to an empty XamlTypeInfo.g.cs file. This will make any type resolution requested by WinRT fail, and your application will mostly likely not run.

In this case, all you need to do is create a dummy Xaml file that will force the generation of the XamlTypeInfo.g.cs, and basically make your layer separation work.

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About me

My name is Jerome Laban, I am a Software Architect, C# MVP and .NET enthustiast from Montréal, QC. You will find my blog on this site, where I'm adding my thoughts on current events, or the things I'm working on, such as the Remote Control for Windows Phone.